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Query: UMLS:C1326912 (tumorigenesis)
 57,481 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tumors that acquire resistance against death stimuli constitute a severe problem in the context of cancer therapy. To determine genetic alterations that favor the development of stress-resistant tumors in vivo, we took advantage of polyclonal tumors generated after retroviral infection of newborn Elambda-MYC mice, in which the retroviral integration acts as a mutagen to enhance tumor progression. Tumor cells were cultivated ex vivo and exposed to gamma-irradiation prior to their transplantation into syngenic recipients, thereby providing a strong selective pressure for pro-survival mutations. Secondary tumors developing from stress-resistant tumor stem cells were analysed for retroviral integration sites to reveal candidate genes whose dysregulation confer survival. In addition to the gene encoding the antiapoptotic Bcl-x(L) protein, we identified the gadd45b locus to be a novel common integration site in these tumors, leading to enhanced expression. In accord with a thus far undocumented role of Gadd45beta in tumorigenesis, we showed that NIH3T3 cells overexpressing Gadd45beta form tumors in NOD/SCID mice. Interestingly and differently to other known 'classical' antiapoptotic factors, high Gadd45beta levels did not protect against MYC-, UV- or gamma-irradiation-induced apoptosis, but conferred a strong and specific survival advantage to serum withdrawal.
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PMID:Gadd45 beta is a pro-survival factor associated with stress-resistant tumors. 1789 Nov 84

Human herpesvirus 8 (HHV-8) infection is associated with the development of Kaposi's sarcoma and primary effusion lymphoma. The cloning of the HHV-8 genome into a bacterial artificial chromosome (BAC) allows researchers to mutate and identify the relative importance of HHV-8 genes essential for growth and replication in tissue culture systems. However, in vivo models to study the impact of such mutations are very limited. Consequently, the objective of this study was to determine whether cells carrying the HHV-8 BAC would form tumors when injected into mice, enabling the use of this model to assess the influence of viral gene mutation on tumorigenesis. To do so, 293T and 293T-E1 cells carrying recombinant HHV-8 were injected into SCID mice and tumor growth was analyzed. Our results clearly show that mice injected with 293T-E1 cells had a significantly higher tumor incidence level as well as increased tumor volumes and weights compared to mice injected with 293T control cells. Cells carrying the HHV-8 genome grew faster and more aggressively in SCID mice than control 293T cells, highlighting the oncogenic properties of HHV-8. The model presented could therefore be used for the identification of HHV-8 genes contributing to tumorigenesis in the context of the entire viral genome.
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PMID:Increased tumorigenicity of cells carrying recombinant human herpesvirus 8. 1794 93

Treatment of the human breast epithelial cells MCF-10F with 17-beta-estradiol (E2) induces transformation and tumorigenesis. E2-transformed MCF-10F cells are known to exhibit progressive loss of ductulogenesis, and invasive and tumorigenic phenotypes. Although DNA amounts and chromatin supraorganization change in E2-transformed MCF cells, no comparative study has yet been undertaken in the resulting cells selected for aggressive invasiveness (C5) and tumor generation in a heterologous host. The aim of this study was thus to determine whether changes in Feulgen-DNA content and chromatin supraorganization are involved during E2-induced transformation and tumorigenesis of the MCF-10F cells. Image analysis was performed for nontransformed and E2-transformed MCF cells, highly invasive cells (C5), and for cell lines (C5-A6-T6 and C5-A8-T8) derived from tumors generated by injection of C5 cells in SCID mice. A decrease in Feulgen-DNA amounts and nuclear sizes induced by E2 treatment was accented with selection of the highly invasive tumorigenesis potential. However, in the tumor-derived cells a high variability in cellular phenotypes resulted inclusively in near-polyploidy. Significant changes in textural parameters, including nuclear entropy, indicated chromatin structural remodeling with advancing tumorigenesis. An increased variability in the degree of chromatin packing states in the E2-transformed MCF cells is followed by reduction in chromatin condensation and in contrast between condensed and noncondensed chromatin in the highly invasive C5 cells and tumor-derived cell lines. Studies on epigenetic mechanisms involving DNA methylation and/or the histone code would contribute to a better interpretation of the chromatin supraorganization changes reported herein.
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PMID:17-beta-estradiol affects nuclear image properties in MCF-10F human breast epithelial cells with tumorigenesis. 1798 33

Previous study reported that the activation of Ras pathway cooperated with E6/E7-mediated inactivation of p53/pRb to transform immortalized normal human astrocytes (NHA/hTERT) into intracranial tumors strongly resembling human astrocytomas. The mechanism of how H-Ras contributes to astrocytoma formation is unclear. Using genetically modified NHA cells (E6/E7/hTERT and E6/E7/hTERT/Ras cells) as models, we investigated the mechanism of Ras-induced tumorigenesis. The overexpression of constitutively active H-RasV12 in E6/E7/hTERT cells robustly increased the levels of urokinase plasminogen activator (uPA) mRNA, protein, activity and invasive capacity of the E6/E7/hTERT/Ras cells. However, the expressions of MMP-9 and MMP-2 did not significantly change in the E6/E7/hTERT and E6/E7/hTERT/Ras cells. Furthermore, E6/E7/hTERT/Ras cells also displayed higher level of uPA activity and were more invasive than E6/E7/hTERT cells in 3D culture, and formed an intracranial tumor mass in a NOD-SCID mouse model. uPA specific inhibitor (B428) and uPA neutralizing antibody decreased uPA activity and invasion in E6/E7/hTERT/Ras cells. uPA-deficient U-1242 glioblastoma cells were less invasive in vitro and exhibited reduced tumor growth and infiltration into normal brain in xenograft mouse model. Inhibitors of Ras (FTA), Raf (Bay 54-9085) and MEK (UO126), but not of phosphatidylinositol 3-kinase (PI3K) (LY294002) and of protein kinase C (BIM) pathways, inhibited uPA activity and cell invasion. Our results suggest that H-Ras increased uPA expression and activity via the Ras/Raf/MEK signaling pathway leading to enhanced cell invasion and this may contribute to increased invasive growth properties of astrocytomas.
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PMID:H-Ras increases urokinase expression and cell invasion in genetically modified human astrocytes through Ras/Raf/MEK signaling pathway. 1838 43

B7-H4, a newly discovered member of B7 family that negatively regulates T cell-mediated immunity, may facilitate tumor progression by undermining host immunity. Recent studies show that brain tumor stem-like cells (TSCs) contribute to tumorigenesis. However, the relationship between B7-H4 and the clinical behavior of brain TSCs remains unclear. In this study, we found that B7-H4 was expressed in cultured tumor cells from human gliomas (n = 5) and medulloblastomas (n = 3). Double immunostaining indicated that B7-H4 was primarily restricted to non-dividing (Ki67(-)) cultured tumor cells. Tumor cells cultured under medium conditions favoring the growth of neural stem cells were able to form primary and secondary spheres, along with expression of neural stem/progenitor cell markers. These cells differentiated into different neural lineages when cultured in differentiation medium, indicating that these cells have TSCs characteristics. Double immunostaining showed that TSCs consisted of proliferative (Ki67(+)) and quiescent (Ki67(-)) cells. We also found that B7-H4 was expressed in a small population of CD133(+) cells sorted by flow cytometry. Interestingly, both CD133(+) and CD133(-) cells were tumorigenic in SCID mice in vivo. However, CD133(+) cells-initiated glioblastomas showed a higher proliferation index, compared to CD133(-) cells-induced glioblastomas in vivo. Secondary glioma cells derived from CD133(+) or CD133(-) cell xenografts expressed B7-H4 as well. Our data suggest B7-H4 is preferentially expressed in non-dividing brain tumor cells and in a subpopulation of brain TSCs, and CD133(-) tumor cells also have the capacity to initiate brain formation in vivo.
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PMID:B7-H4 is preferentially expressed in non-dividing brain tumor cells and in a subset of brain tumor stem-like cells. 1847 83

Colon cancer stem cells are believed to originate from a rare population of putative CD133+ intestinal stem cells. Recent publications suggest that a small subset of colon cancer cells expresses CD133, and that only these CD133+ cancer cells are capable of tumor initiation. However, the precise contribution of CD133+ tumor-initiating cells in mediating colon cancer metastasis remains unknown. Therefore, to temporally and spatially track the expression of CD133 in adult mice and during tumorigenesis, we generated a knockin lacZ reporter mouse (CD133lacZ/+), in which the expression of lacZ is driven by the endogenous CD133 promoters. Using this model and immunostaining, we discovered that CD133 expression in colon is not restricted to stem cells; on the contrary, CD133 is ubiquitously expressed on differentiated colonic epithelium in both adult mice and humans. Using Il10-/-CD133lacZ mice, in which chronic inflammation in colon leads to adenocarcinomas, we demonstrated that CD133 is expressed on a full gamut of colonic tumor cells, which express epithelial cell adhesion molecule (EpCAM). Similarly, CD133 is widely expressed by human primary colon cancer epithelial cells, whereas the CD133- population is composed mostly of stromal and inflammatory cells. Conversely, CD133 expression does not identify the entire population of epithelial and tumor-initiating cells in human metastatic colon cancer. Indeed, both CD133+ and CD133- metastatic tumor subpopulations formed colonospheres in in vitro cultures and were capable of long-term tumorigenesis in a NOD/SCID serial xenotransplantation model. Moreover, metastatic CD133- cells form more aggressive tumors and express typical phenotypic markers of cancer-initiating cells, including CD44 (CD44+CD24-), whereas the CD133+ fraction is composed of CD44lowCD24+ cells. Collectively, our data suggest that CD133 expression is not restricted to intestinal stem or cancer-initiating cells, and during the metastatic transition, CD133+ tumor cells might give rise to the more aggressive CD133(- )subset, which is also capable of tumor initiation in NOD/SCID mice.
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PMID:CD133 expression is not restricted to stem cells, and both CD133+ and CD133- metastatic colon cancer cells initiate tumors. 1849 83

Tumor cell-associated chemokine receptors play distinct roles in cancer biology, including enhancement of lymph node (LN) metastasis. To determine if CCR7 influences tumor formation in skin, we inoculated B16 cells transduced with CCR7 and luciferase (CCR7-luc-B16) or with retroviral vector and luciferase (pLNCX2-luc-B16) into ear skin and footpads of wild-type (WT) mice. In contrast to pLNCX2-luc-B16 cells, 97% of CCR7-luc-B16 cell-inoculated mice formed skin tumors as well as cervical LN metastases by Day 21 following ear inoculation. CCR7-expressing and control B16 cells, however, formed tumors of similar size and with high-efficiency in SCID-beige mice. Cells from both lines accumulated in the skin of WT mice in similar numbers until Day 7. By Day 11, however, control cells decreased tenfold, whereas CCR7-luc-B16 cells formed small tumor nodules. Tumor cells were infrequently detected in draining cervical LNs up to 11 days after injection of both cell lines, but stable nodal metastases were only observed after CCR7-luc-B16 ear tumors had been established (Day 21). ELISPOT assays revealed that IFN--producing cells in draining LNs from CCR7-luc-B16-injected ears were reduced through Day 7. After footpad injection, tumor formation by CCR7-expressing B16 cells was enhanced only with small, initial tumor cell inocula. With larger inocula, tumor formation was equivalent, but the numbers of tumor-infiltrating leukocytes were reduced by approximately sixfold in CCR7-B16 tumors compared with pLNCX2-B16 tumors of equal size. IFN- and CXCL10 were reduced 35- and sixfold, respectively, in CCR7-B16 cell tumors (vs. control tumors). Thus, CCR7 expression enhances tumorigenesis in addition to facilitating LN metastasis.
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PMID:CCR7 regulates B16 murine melanoma cell tumorigenesis in skin. 1851 42

The cancer stem cell hypothesis proposes that cancers arise in stem/progenitor cells through disregulation of self-renewal pathways generating tumors, which are driven by a component of 'tumor-initiating cells' retaining stem cell properties. The HER2 gene is amplified in 20-30% of human breast cancers and has been implicated in mammary tumorigenesis as well as in mediating aggressive tumor growth and metastasis. We demonstrate that HER2 overexpression drives mammary carcinogenesis, tumor growth and invasion through its effects on normal and malignant mammary stem cells. HER2 overexpression in normal mammary epithelial cells (NMEC) increases the proportion of stem/progenitor cells as demonstrated by in vitro mammosphere assays and the expression of stem cell marker aldehyde dehydrogenase (ALDH) as well as by generation of hyperplastic lesions in humanized fat pads of NOD (nucleotide-binding oligomerization domain)/SCID (severe combined immunodeficient) mice. Overexpression of HER2 in a series of breast carcinoma cell lines increases the ALDH-expressing 'cancer stem cell' population which displays increased expression of stem cell regulatory genes, increased invasion in vitro and increased tumorigenesis in NOD/SCID mice. The effects of HER2 overexpression on breast cancer stem cells are blocked by trastuzumab in sensitive, but not resistant, cell lines, an effect mediated by the PI3-kinase/Akt pathway. These studies provide support for the cancer stem cell hypothesis by suggesting that the effects of HER2 amplification on carcinogenesis, tumorigenesis and invasion may be due to its effects on normal and malignant mammary stem/progenitor cells. Furthermore, the clinical efficacy of trastuzumab may relate to its ability to target the cancer stem cell population in HER2-amplified tumors.
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PMID:HER2 regulates the mammary stem/progenitor cell population driving tumorigenesis and invasion. 1859 32

We recently reported on continuous tumor-stroma interactions essentially contributing to chemoresistance of pancreatic ductal adenocarcinoma (PDAC) cells. As demonstrated here, long-term coculture with pancreatic myofibroblasts representing the main stromal compartment of PDAC resulted in a chemoresistant phenotype in the pancreatic ductal epithelial cell line H6c7 as well as in the chemosensitive PDAC cell line T3M4. This involved a reduced expression of caspases and the caspase inducing transcription factor STAT1, both caused by diminished gene transcription. The DNA-methylation inhibitor 5-azadeoxycytidine enhanced caspase and STAT1 expression in cocultured H6c7 and T3M4 cells along with an increased chemosensitivity, indicating a role for CpG DNA-hypermethylation in the downregulation of these crucial apoptosis mediators. Cocultured H6c7 and T3M4 cells exhibited elevated nuclear levels of DNA-methyltransferase-1 (DNMT1). Silencing of DNMT1 expression by siRNA increased expression of caspases and STAT1 and restored chemosensitivity. In SCID mice, tumors arising from coinoculated T3M4 cells and myofibroblasts (co-tumors) responded less towards chemotherapy than mono-tumors, exhibiting decreased apoptosis, no remission and reduced expression of caspases and STAT1. These data underscore the role of myofibroblasts in chemoresistance of PDAC and point to the importance of caspases as central target structures of epigenetic regulation in this scenario. Furthermore, an activated microenvironment might apparently promote the manifestation of chemoresistance already in premalignant precursor cells at early stages of PDAC tumorigenesis.
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PMID:Role of myofibroblasts in innate chemoresistance of pancreatic carcinoma--epigenetic downregulation of caspases. 1864 62

Our previous studies indicate that reduction of lipocalin 2 (mouse 24p3) expression by either anti-sense or siRNA approaches strongly reduces the overgrowth of BCR-ABL+ mouse myeloid 32D in marrow and spleen of NOD/SCID mice. In this study, we used the mouse bone marrow transplant model to further explore the role of 24p3 in BCR-ABL-induced leukemia. Consistent with our previous findings, when using non-irradiated mice as recipient, donor marrow cells expressing BCR-ABL but lacking 24p3 did not cause leukemia or any disease after 75 days, whereas all mice receiving wild type BCR-ABL donor cells died with CML-like disease. An agar clone of the BCR-ABL+ human CML cell line K562 (C5) that secretes relatively high levels of lipocalin 2 (human NGAL) induced suppression of hematopoiesis in spleen and marrow of mice, leading to early death in contrast to parental K562 or K562 clone (C6) expressing low amounts of NGAL. Compared with K562 cells, overexpressing NGAL in K562 led to a higher apoptosis rate and an atrophy phenotype in the spleen of the inoculated mice. Plasma from both leukemic mice and CML patients showed elevated lipocalin 2 levels compared with healthy individuals. Moreover, we found that a primary stable cell line from wild-type mouse marrow cells expressing BCR-ABL caused solid tumors in nude mice whereas a similar BCR-ABL+ cell line from 24p3 null mice did not. These findings demonstrate that lipocalin 2 has at least two functions related to tumorigenesis, one involving apoptosis induction of normal hematopoietic cells and the other being tissue invasion by leukemia cells.
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PMID:Lipocalin 2 is required for BCR-ABL-induced tumorigenesis. 1866 64


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